Stents are vascular scaffolds that are positioned in diseased vessel segments to support the vessel walls. During angioplasty, stents are used to repair and reconstruct blood vessels. Placement of a stent in the affected arterial segment prevents elastic recoil and closing of the artery. Stents also prevent local dissection of the artery along the medial layer. Physiologically, stents may be placed inside the lumen of any space, such as an artery, vein, bile duct, urinary tract, alimentary tract, tracheobronchial tree, cerebral aqueduct or genitourinary system. Stents may also be placed inside the lumen of non-human animals, such as primates, horses, cows, pigs and sheep.
In general, there are two types of vascular scaffolds or stents: self-expanding and balloon-expandable. Self-expanding stents automatically expand once they are released and assume a deployed, expanded state. A self-expanding stent is placed in the vessel by inserting the stent in a compressed state into the affected region, e.g., an area of stenosis. Compression or crimping of the stent can be achieved using crimping equipment (see, http://www.machinesolutions.org/stent_crimping.htm, April, 2009). The stent may also be compressed using a tube that has a smaller outside diameter than the inner diameter of the affected vessel region. Once the compressive force is removed or the temperature raised, the stent expands to fill the lumen of the vessel. When the stent is released from confinement in the tube, the stent expands to resume its original shape, in the process becoming securely fixed inside the vessel against the wall.
A balloon-expandable stent is expanded using an inflatable balloon catheter. Balloon-expandable stents may be implanted by mounting the stent in an unexpanded or crimped state on a balloon segment of a catheter. The catheter, after having the crimped stent placed on it, is inserted through a puncture in a vessel wall and moved through the vessel until it is positioned in the portion of the vessel that is in need of repair. The stent is then expanded by inflating the balloon catheter against the inside wall of the vessel. Specifically, the stent is plastically deformed by inflating the balloon so that the diameter of the stent is increased and the stent expanded.
There are limitations common to many stents. For example, stents whose bodies are made from polymeric material often suffer from excessive recoil and low radial strength. There is a need for improved stent design that addresses these problems.